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Structural basis for complement factor I control and its disease-associated sequence polymorphisms.

Pietro Roversi1, Steven Johnson, Joseph J E Caesar

  • 1Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom.

Proceedings of the National Academy of Sciences of the United States of America
|July 20, 2011
PubMed
Summary
This summary is machine-generated.

The crystal structure of human factor I (fI), a complement regulator, reveals it circulates in an inactive, zymogen-like state. This structure explains how fI is regulated and how mutations cause disease.

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Area of Science:

  • Immunology
  • Structural Biology
  • Biochemistry

Background:

  • The complement system is crucial for innate and adaptive immunity.
  • Effective complement regulation is vital for preventing and managing diseases.
  • Human factor I (fI) is a key enzyme in complement regulation.

Purpose of the Study:

  • To determine the crystal structure of human factor I (fI).
  • To understand the mechanism of complement regulation by fI.
  • To elucidate the molecular basis of fI-associated diseases.

Main Methods:

  • X-ray crystallography to determine the 3D structure of human fI.
  • Functional analysis of fI mutants.
  • Mapping functional data onto the determined crystal structure.

Main Results:

  • Human fI circulates in a proteolytically inactive, zymogen-like state.
  • The heavy chain allosterically inhibits the light chain's activity in the inactive fI.
  • Formation of a ternary complex releases inhibition, enabling fI to cleave C3b/C4b.

Conclusions:

  • The determined structure explains the auto-inhibited state of circulating fI.
  • The findings provide a molecular model for complement regulation by fI.
  • The study elucidates the basis of disease-associated polymorphisms in fI and its cofactors.